OP linked this article which explains the evaporation: http://www.npr.org/sections/thesalt/2017/10/13/557607443/with-ok-from-epa-use-of-controversial-weedkille

OP linked this article which explains the evaporation: http://www.npr.org/sections/thesalt/2017/10/13/557607443/with-ok-from-epa-use-of-controversial-weedkiller-is-expected-to-double http://www.npr.org/sections/thesalt/2017/10/13/557607443/wit... Bob Scott, a weed scientist at the University of Arkansas, recently showed me some experiments that he and his colleagues conducted. They sprayed trays of soil with dicamba, then placed those trays in a field of soybeans far from any dicamba spraying. The soybean plants next to the dicamba-treated soil showed clear signs of exposure to the chemical. "We had a lot of volatility in these trials, a lot of movement" in unpredictable directions, Scott says. It wasn't what they were hoping to see, Scott says, but the results "do help explain why we had 966 complaints in our state."